Pathway · 7 proteins
Protein translocation
Sec/Tat annotations identify protein-export machinery.
How it works
- Sec and Tat annotations describe alternative protein-translocation systems. SecY, SecE and SecG form a representative channel complex, with SecA-associated export and accessory factors; TatA-family and TatC components belong to a different route.
- Sec-mediated export can move an unfolded chain through the membrane with ATP-dependent SecA activity. Tat instead accommodates selected folded substrates bearing appropriate targeting signals and uses membrane energization.
- These are separate routes, not two consecutive stages. A complete route also depends on substrate signals, membrane integrity, energy supply and correct partner assembly.
Grouped by the atlas’s curated pathway map. The table order is not a proven reaction order.
Its proteins
| Protein | EC | Reaction (UniProt) | Metal or cluster | Amino acids | Certainty |
|---|---|---|---|---|---|
| Protein translocase subunit SecY | — | — | — | 429 | Step named |
| Protein-export membrane protein SecG | — | — | — | 100 | Step named |
| Sec translocon accessory complex subunit YajC | — | — | — | 102 | Step named |
| Sec-independent protein translocase protein TatC | — | — | — | 240 | Step named |
| Protein translocase subunit SecF | — | — | — | 288 | Step named |
| Protein translocase subunit SecA | 7.4.2.8 | ATP + H2O + cellular proteinSide 1 = ADP + phosphate + cellular proteinSide 2. | — | 984 | Step named |
| Protein translocase subunit SecD | — | — | — | 501 | Step named |
Also part of this pathway
These proteins are described under another pathway, but also take part here.
| Protein | EC | Reaction (UniProt) | Metal or cluster | Amino acids | Certainty |
|---|---|---|---|---|---|
| Twin-arginine translocation signal domain-containing proteinHome: Not yet placed in a pathway | — | — | — | 124 | System only |
Origins
How could proteins cross or enter the membrane before the Sec channel existed?
None of the books searched discusses a prebiotic route to protein translocation.
Tan and Stadler stress that most proteins work only as parts of larger assemblies, like pieces of a construction set. The Sec channel is an example: a membrane protein complex that itself has to be inserted into the membrane by the machinery it forms. Seven proteins of the minimal set serve this pathway.
From the books: Tan & Stadler, The Stairway to Life, PDF p. 218.
The wider question for this part of the cell: origins for building proteins and folding them.
Sources
- Atlas pathway grouping from the VF5 reference-genome system map (Deckert et al. 1998; Braakman & Smith 2014)
Other pathways in this group: Ribosomal subunits · Translation interface · RNA maturation · Translation cycle · Protein turnover · Folding and stabilization · Recycling and rescue · Early folding support · Protein targeting · Ribosome · Protein export · Not yet placed in a pathway